I. Technical Field
This invention pertains to telecommunications, and particularly to the construction and operation of base stations which communicate with wireless terminals over an air interface.
II. Related Art and Other Considerations
In a typical cellular radio system, wireless user equipment units (UEs) communicate via a radio access network (RAN) to one or more core networks. The user equipment units (UEs) can be mobile stations such as mobile telephones (“cellular” telephones) and laptops with mobile termination, and thus can be, for example, portable, pocket, hand-held, computer-included, or car-mounted mobile devices which communicate voice and/or data with radio access network. Alternatively, the wireless user equipment units can be fixed wireless devices, e.g., fixed cellular devices/terminals which are part of a wireless local loop or the like,
The radio access network (RAN) covers a geographical area which is divided into cell areas, with each cell area being served by a base station (some times called a “NodeB”). A cell is a geographical area where radio coverage is provided by the radio base station equipment at a base station site. Each cell is identified by a unique identity, which is broadcast in the cell. The base stations communicate over the air interface (e.g., radio frequencies) with the user equipment units (UE), mobile stations, mobile termiawithin range of the base stations. In the radio access network, several base stations are typically connected (e.g., by landlines or microwave) to a radio network controller (RNC). The radio network controller, also sometimes termed a base station controller (BSC), supervises and coordinates various activities of the plural base stations connected thereto. The radio network controllers are typically connected to one or more core networks.
In some radio access network arrangements, plural radio base stations may serve a common geographical region, but be operated differently, e.g., at different power levels. For example, a first radio base station (e.g., a macro radio base station) may operate with standard or even high transmit power to serve a fairly large geographical area (a “macro” cell). Such a radio base station endeavors to serve users (e.g., user equipment units (UEs)) of the cell, even users who may be geographically situated near an edge of the cell.
Usually not all users are located proximate a boundary or edge of the cell. In fact, some of the users within the geographical boundary of the macro cell may be served by a smaller cell or “micro” or “pico” cell, essentially contained within the macro cell. The smaller cell can be served by a radio base station which operates with a smaller transmit power. The cell structure of such a network design arrangement using radio base stations operating with different power (providing, e.g., macro and micro cells) is often referred to as underlay/overlay cells.
One of the most critical design parameters when designing a radio base station is power efficiency of the radio base station. As an example, for a telecommunications system known as Global System for Mobile communications (GSM), a good efficiency rating for transistors of a power amplifier (and thus the power amplifier itself) is about 50%, and probably more like 40% for a typical system. Yet the overall efficiency of a radio base station node is typically more like 10%. Thus, while some efficiency losses at the radio base station are thus attributable to the power amplifiers, other and perhaps more significant efficiency losses are sustained by other functions such as filtering and combining.
Combining is the process which facilitates two carriers (e.g., two different frequencies carrying a modulated information signal) using a single, shared antenna, rather than two separate antennas. Often the two carriers which are combined and transmitted over the shared antenna serve a same sector of a cell. For example, a typical GSM radio base station may be configured so that a cell has three sectors, each sector employing four carriers. Therefore, combining enables two carriers to be transmitted from each antenna, so that only six antennas rather than twelve antennas can be used for the twelve carriers of the base station.
Certain measurement units pertaining to power are briefly explained prior to discussing further the power inefficiency in a conventional radio base station. In conventional nomenclature, “dBm” is an abbreviation for the power ratio in decibel (dB) of the measured power referenced to one milliwatt (mW). It is used in radio, microwave and fiber optic networks as a convenient measure of absolute power because of its capability to express both very large and very small values in a short form. dBm (or dBmW) and dBW are independent of impedance. Zero dBm equals one milliwatt. A 3 dB increase represents roughly doubling the power, which means that 3 dBm equals roughly 2 mW. For a 3 dB decrease, the power is reduced by about one half, making −3 dBm equal to about 0.5 milliwatt. To express an arbitrary power P as x dBm, Equation 1 should be used. Or go in the other direction, Equation 2 should be used.x=10 log10(P/Plmw)  Equation 1P=(Plmx)10(x/10)  Equation 2
An example of power inefficient of a typical, representative conventional radio base station 120 is illustrated in FIG. 1. The portions of radio base station 120 shown in FIG. 1 comprise power amplifiers 1241 and 1242 which feed a hybrid combiner 130. The output of the hybrid combiner 130 is applied to a duplex filter 132, which in turn feeds an antenna 122. The carriers driven by power amplifiers 1241 and 1242 are both applied with 46 dBm (40 Watts power) to hybrid combiner 130. The power loss of each carrier incurred through hybrid combiner 130 is 3.5 dB. The combined signal exiting hybrid combiner 130 suffers a 1.5 dB loss in duplex filter 132. As a result, the antenna 122 has two carrier signals, both being 41 dBm for a total antenna output power of 25 W. Of the 200 Watts in power applied to the power amplifiers 1221 and 1222, 175 Watts of heat is discharged through the circuit, e.g., through load 156, through power amplifiers 1241 and 1242, and through duplex filter 132.
As can be seen from the foregoing example, power inefficiency produces not only power consumption problems for a radio base station, but also heat dissipation issues. Heat dissipation is particularly important since as many as six antennas may be operating at a base station, with the consequence that the structure and heat of FIG. 1 may have a multiple of six. In order to generate the desired transmit output power of 20 W, such a base station running at full performance may generate about 2 kW of heat.
To assure operational integrity of a base station, the large amount of heat lost through inefficiency needs to be handled or dissipated. Ways of handling or coping with such a large amount of heat byproduct include rather large cooling fins and high performance noisy fans. Other cooling measures for an outdoor radio base station might include either a heat exchanger and/or combined air conditioning system (using, e.g., compressors). These cooling mechanisms and measures significantly increase cost of construction and operation of the radio base station, increasing power consumption and (even more so) size and weight and of the radio base station node. These ramifications are adverse to the environment and costly to the radio base station operator.
What is needed, therefore, and an object of the present invention, are one or more of apparatus, systems, methods and techniques for managing power usage and/or output of a radio base station.